The present invention discloses a process to recover betaines from electrodialysis waste streams from betaine production processes by pressure driven membrane processes.
The synthesis of betaines very often goes along with the production of stoichiometric amounts of organic or inorganic salts in the reaction mixture. Usually the products are further separated from the salts by various purification methods such as distillation, extraction, crystallization, electrodialysis or other unit operations. Every purification/separation process inevitably suffers from product losses.
Electrodialysis (ED) is a membrane technology used to purify organic products in liquid mixtures. The ED can be used to reduce the salt concentration in a mixture in a discretionary way and furthermore for the selective removing of organic compounds contained in a liquid solution. The driving force for this separation is an electric field over the membranes. Due to diffusion phenomena and/or osmotic pressure, product losses into the waste stream are inevitable. (see EP 0163222 B2, example 1c, disclosing a yield of 82%)
Pressure driven membrane processes such as Reverse Osmosis, nanofiltration, ultrafiltration or microfiltration can be applied to concentrate/retain organic compounds. The salts will only be partially concentrated/retained, depending on the type of membrane used.
The present state of the art suffers from several major disadvantages. The product losses in the waste stream due to e.g. diffusion and/or osmotic pressure decrease the yield of the ED process and contribute to the organic freight (total organic carbon, TOC) of the waste stream. Consequently, the waste stream can frequently not be properly treated in a biological waste stream treatment plant if the product is poorly biodegradable, requiring a subsequent incineration step with prohibitive costs for the industrial production. Thus, there is a need for a novel method for the minimization of product losses during the purification of betaine compounds.